Composite materials are frequently used to form various structural components in applications where relatively low weight and high mechanical strength is desired. For example, composite materials are widely used in a variety of commercial and military aircraft, terrestrial vehicles and consumer products. A composite material is generally comprised of a network of reinforcing fibers and a polymeric resin that substantially wets the reinforcing fibers to form an intimate contact between the resin and the reinforcing fibers. The composite material may then be formed into a structural component by a variety of known forming methods, such as an extrusion process, a molding process, or other suitable forming processes.
In general, the composite fabrication process must be carefully monitored in order to obtain a composite material having the desired mechanical properties. For example, the composition of the resin and the reinforcing fiber must be carefully controlled so that the resin and the reinforcing fiber are combined so that the resin properly bonds to the fibers, and that no voids are formed within the composite material. The material may then be molded into a desired shape and cured, so that the material develops the desired mechanical properties and retains the desired shape. The degree of cure, in particular, may have a pronounced effect on material properties such as the strength and modulus. Typically, over-curing the material generates excessive cross-linking within the material, which may make the material excessively brittle. Correspondingly, under-curing the material may result in a molded component that exhibits insufficient rigidity.
One difficulty associated with the fabrication of composite materials is that various properties of the molded component must be determined by destructively testing the component. Alternately, a standard test sample may be fabricated and the test sample may be destructively tested to determine the mechanical properties of the composite material. The chemical properties of the composite material may be inferred from the outcome of the destructive test. In another known method, a sample of the composite material is removed and exposed to a solvent that dissolves the resin. Liquid chromatography is then used to determine the constituents present in the solvent. Since the sample is usually cut from the molded component, the remainder of the component must be discarded. Accordingly, inspection of composites using destructive testing methods may be expensive and wasteful.
Accordingly, what is needed in the art are apparatus and methods for determining the chemical properties of a resin material in a non-destructive manner.